Rheumatoid arthritis (RA) is a chronic inflammatory disease accompanied with polyarthritis as a main lesion and a high prevalence of collagenosis (1% of the global population). Cause of the disease is unknown, but the disease is believed to be the result of environmental factors, such as infection, in addition to genetic factors. Correlation between development of symptom and HLA DR4 and the existence of T cells in synovial tissue suggest that abnormalities in T cells participate in the pathophysiology. Moreover, abnormalities in immunity, such as hyperglobulinemia due to polyclonal activation of B cells and appearance of autoantibodies, are observed. To date, model mice for autoimmune disease accompanied with arthritis and arthritis-induced model mice have been employed to analyze the pathophysiology of the disease, and transgenic mice and spontaneous mice which present arthritis have been reported in recent years. For example, the following are typical arthritis model mice reported to date.
1. Arthritis Model Mouse Induced by Antigenic Sensitization Etc.
The arthritis is induced by immunization of an intra-articular autoantigen with a strong adjuvant, or injection of microbial antigen crossreactive to the intra-articular autoantigen. Unlike RA, the symptoms are observed in a short period of time after the sensitization. The microbial antigen used is epidemiologically unrelated to human RA.
(1) Type II Collagen (IIC)-Induced Arthritis Model Mouse (Nature, 666–668, 1980. J. S. Courtenay et. al.)
Procedures: DBA/1J mouse is immunized with an emulsion prepared from bovine IIC and Freund's complete adjuvant. Three weeks later, bovine IIC and Freund's incomplete adjuvant are boosted, and the arthritis develops in 1–2 weeks.
Features: Unlike the adjuvant arthritis in rat, which is similar to Reiter's syndrome in human, this model is considered to be more relevant to human RA, in that it has no cutaneomucosa and organ involvement, and observations of the tissues resemble closely those in human RA. Cellular immunity and humoral immunity participate in this model mouse, and therefore, the arthritis can be induced with an anti-collagen monoclonal antibody. IL-6 is a precipitating factor (J. Exp. Med. 187, 461–468, 1998, Arthritis Rheumat. 42, 1635–1999). This model mouse is useful in producing various knock-out mice to identify gene products that aggravate or relieve arthritis.
Problems: Non-physiological operations for immunization are required. Deterioration-improvement pattern as observed in human RA is not observed. Rheumatoid factor (RF) is not produced.
(2) Antigen-Induced Arthritis Mouse (Arthritis Rheum. 20, 841–850, 1977)
Procedures: The arthritis is induced by sensitizing a mouse with an antigen, such as methylated bovine serum albumin, and followed by boosting of the antigen intra-articularly.
Features: IL-6 is a precipitating factor (Proc. Natl. Acad. Sci. USA, 95, 8222–8226, 1998). C57BL/6 and Balb/c mouse are used.
(3) CpG-Induced Arthritis Mouse (Nature Medicine, 5, 702–705, 1999, Arthritis Rheum. 43, 356–364, 2000)
Procedures: The arthritis is induced by intra-articular injection of CpG, which is a bacterial DNA having immuno-stimulating action.
Features: Macrophage precipitates in the arthritis. Local production of TNFα, IL-12, IL-1β, MCP-1, and RANTES in a joint, and increased production of blood IgG and IL-6 are involved. The arthritis can be induced in C57BL/6, Balb/c, C3H/HeN mouse, etc.
2. Spontaneous Arthritis Model Mouse
(1) MRL-lpr/lpr and gld Mouse
Features: Abnormal proliferation of T cells, SLE-like lesion, arthritis and production of RF observed in this model are similar to those observed in human RA. It has been clearly shown that the main abnormalities are caused by Fas/Fas ligand.
Problems: Influences of a hereditary background involve symptoms that do not develop in C57BL/6, C3H, and AKR etc., and thus, development of the arthritis is not only due to abnormality in FAS/FAS ligand. Prolonged observation and analysis of progression of the disease are difficult, since the animal dies at about six-months old, because of abnormal multiplication of T cells.
(2) SKG Mouse (Reference: Molecular Medicine, vol 34, Extra Number, Immunity 1997–1998, p214–221)
Features: Symptoms of the arthritis are marked in comparison with MRL-lpr/lpr mouse. No abnormal proliferation of T cells is involved. Hyperglobulinemia is presented, and autoantibodies such as anti-IIC antibody and RF of IgM class are produced. The abnormalities in T cells are considered as the main cause because arthritis develops in a normal mouse by transplantation of T cells from a mouse presenting arthritis. This SKG mouse is derived from Balb/c mouse.
Problems: The cause of development of the disease is unknown.
3. Genetic-Engineering Model Mouse
Since the arthritis develops as a result of genetic engineering (gene transfer, knock-out, knock-in), the cause of development of the disease is clear.
(1) TNFα Transgenic Mouse (EMBO J. 10, 4025, 1991)
Features: This is a model mouse wherein the arthritis is caused by overproduction of cytokines. It has been shown that the arthritis is relieved with the anti-TNF antibody. In the hereditary background of DBA/1, the arthritis is more serious (J. Immunol. 159, 2867–2876, 1997). IL-1β and IL-6 are produced by cells in synovial membrane. The cells in synovium tissue are mainly neutrophils, and other fibroblasts and endothelial cells, and there is little participation of lymphocytes.
(2) HTLV-1Tax Transgenic Mouse (Science, 253, 1026–1028, 1991, J. Immunol, 155, 1588–1598, 1995, J. Immunol, 161, 6592–6598, 1998)
Features: Production of cytokines such as TNF, IL-1, and IL-6 are increased, because of the over-expression of Human T Cell Leukemia Virus Type 1 gene tax. Hyperglobulinemia is presented, and RF, anti-IIC and anti-DNA antibodies are produced. Development of symptoms is not related to H-2 haplotype. The incident is high in order of Balb/c, C3H/HeN, and C57BL/6.
(3) IL-1 Receptor Antagonist Knock-Out Mouse: (J. Exp. Med. 191, 313–320, 2000)
Features: The arthritis is developed in the hereditary background of Balb/c. The incident is low in C57BL/6. The arthritis develops, because of the deficiency of a molecule which negatively controls a citokine signal. Local production of IL-6 and IL-1β increases in a joint. Hyperglobulinemia is presented, and RF, anti-IIC and anti-DNA antibodies are produced.
(4) T Cell Antigen Receptor Transgenic Mouse (Cell, 87, 811–822, 1996, Immunity 10, 451–461, 1999, Science, 286, 1732–1735, 1999)
Features: A transgenic mouse, which has a T cell receptor (α, β) that I-Ak-restrictively recognizes bovine pancreas ribonuclease peptide R41-61, is crossed with a NOD mouse to develop arthritis. Neutrophilic infiltration is observed in a joint space. Hyperglobulinemia and anti-DNA antibodies are observed, but RF is not observed. The arthritis is possible to be developed in a healthy mouse with introduction of the antibody in the serum of a mouse presenting arthritis, and it has been shown clearly that the antigen, which is recognized by this antibody and T cells of the mouse presenting arthritis, is such antigen as referred to as Glucose-6-Phosphate Isomerase (GPI). It is associated with mechanisms wherein ribonuclease-specific T cells recognize GPI combined with I-Ag7 inherent in NOD mouse and are activated to induce a inflammatory response specific to a join.
The model mice described above present the symptoms of arthritis by the mechanisms that are respectively different, such that they reflect that the pathogenesis of human RA, which is caused by many factors. Although all pathophysiology shown in these model mouse are not completely consistent with those in human RA, it is apparent that a new arthritis model mouse would be useful in analysis of a certain aspect of the onset of RA, in view of the fact that multiple factors participate in development of RA.
Participation of IL-6 in the pathophysiology of arthritis has been shown not only by clinical observations, but also in the model mice described above. However, there is no case wherein the arthritis is actually developed in any IL-6 related genetic mouse reported to date. Moreover, although it has been produced by many model mice presenting arthritis, which have been gene-engineered to enhance the production of cytokines and their function, there are few among these model mice that are suitable for analysis of the functional abnormalities of T cells. The T cell antigen receptor transgenic mouse described above could not demonstrate how self-reactivity T cell clones are selected from the T cell repertories to break the self-tolerance. Although abnormalities such as T cell selection may participate in SKG mouse, it is difficult to investigate the cause of the disease because of spontaneous development of the symptoms.
gp130 is a membrane protein having a molecular weight of 130 kDa and a common receptor subunit for L-6 family citokines. gp130 participates in not only IL-6 signal transmission but also signal transmissions of other IL-6 family citokines: leukemia inhibitory factor (LIF), ciliary neurotrophic factor (CNTF), oncostatin M (OSM), Interleukin-11 (IL-11), and cardiotrophin-1 (CT-1). (Hirano, T. et al. (1997) Cytokine Growth Factor Rev. 8, 241–52).
IL-6 family cytokine binds to a receptor, and thereby homodimer formation between gp130 proteins or heterodimer formation between gp130 protein and another gp130 related factor is induced. Subsequently, a tyrosine residue on the gp130 protein is phosphorylated, and SHP2 (SH2 domain contained protein tyrosine phosphoatase 2) is associated with the phosphorylated tyrosine residue, and the SHP2 is further phosphorylated to transmit signals downstream. The phosphorylation of SHP2 necessitates phosphorylation of tyrosine 759 in human gp130 (Hirano, T. et al. (1997) Cytokine Growth Factor Rev. 8, 241–52). Furthermore, it was reported recently that the molecule called SOCS-3 (suppressor of cytokine signaling-3), which is responsible for feedback control of the cytokine signal, binds to this tyrosine 759 of human gp130 protein (Proc. Natl. Acad. Sci. USA, 2000, 97, 6493–8).
The amino acid sequence of human gp130 protein is known, and cDNA encoding the human gp130 protein has been reported (Hibi, M et al., (1990) Cell 63, 1149–57). Also, the amino acid sequence of mouse gp130 is known, and cDNA encoding the mouse gp130 has been reported (Saito et al., (1992) J. Immunol. 148, 4066–71).